The present invention relates to vinylidene chloride resin compositions which are particularly suitable for producing substantially transparent moldings having improved gas barrier properties.
Over many years, moldings of vinylidene chloride resins have been used for producing packaging films for foods and the like products due to their transparency and to their excellent barrier resistance to gas such as oxygen and to water vapor.
In the industrial production of such vinylidene chloride resin moldings, plasticizers are generally added to the resin in order to lower its softening point and facilitate its processing as well as to inhibit heat deterioration occurring during the processing and impart to the moldings desirable properties such as flexibility and toughness.
However, the use of such additives, which generally exist as a liquid at temperatures where the moldings are used or kept in storage, tends to deteriorate the gas barrier properties of the vinylidene chloride resin moldings. Therefore, although the quantity of plasticizers, and other additives added to the resin, is generally restricted to the lowest level to meet the desired purpose, it cannot be concluded that the vinylidene chloride resin moldings which are now commercially available in the market are fully exhibiting their advantageous features due to reduction in the gas barrier properties derived from the use of such plasticizers.
To offset the shortcoming mentioned above, it has been proposed to add a rubber-like material such as a butadiene copolymer or ethylene-vinyl acetate copolymer to the vinylidene chloride resin in place of the plasticizer or a part thereof. However, if such a rubber-like material is to be used as a substitute for the plasticizer or to make up for the decrease in the quantity of the plasticizer, a relatively large quantity is required to be added because of its poor stabilizing ability. Further, since the compatibility of these rubber-like materials with the vinylidene chloride resins is far inferior to that of plasticizers, the transparency of the resultant moldings is lost if such rubber-like materials are added in a large quantity. Thus, so far as the conventional rubber-like materials are used, it has been difficult to obtain moldings which are satisfactory with regard to both transparency and gas barrier properties.
It is, therefore, an object of the present invention to further improve the gas barrier properties of such vinylidene chloride resin moldings without sacrificing the transparency thereof.